By coupling a nonlinear system, such as an atom, to the electromagnetic field, it is possible to create Fock states (eigenstates of the harmonic oscillator). (Top) Brune et al. send atoms (left) into a cavity (center). The atoms are prepared with pulse to be in a superposition of states and before they enter the cavity. The relative phase between these states, which is converted to probability amplitudes for and with pulse when the atoms exit the cavity, depends on the number of photons in the cavity. (Bottom) In place of a cavity, Wang et al. create an electromagnetic field in a microwave resonator (blue). A superconducting qubit, acting as an artificial atom, couples to the center conductor.